1. Field of the Invention
This invention relates to solid electrolytic capacitors and methods for manufacturing the same.
2. Description of Related Arts
FIG. 10 shows in cross section the structure of a conventional solid electrolytic capacitor.
As shown in this figure, a conventional solid electrolytic capacitor 120 has a capacitor element composed of: an anode 101 made of a valve metal; an anode lead 102 provided so that one end portion 102a thereof is embedded into the anode 101 and the other end portion 102b extends out of the anode 101; a dielectric layer 13 formed by anodizing the anode 101 and a portion of the anode lead 102; an electrolyte layer 104 formed on the dielectric layer 103; and a cathode extraction layer 105 formed on the electrolyte layer 104. The anode 101 and the anode lead 102 are joined and integrated together by embedding the anode lead 102 into a powder body made of a valve metal to extend at the other end portion 102b out of the powder body, forming the powder body into an anode 101 having the outer shape of a rectangular box, and sintering it.
An anode terminal 107 is attached to the other end portion 102b of the anode lead 102, and a cathode terminal 109 is attached on a portion of the cathode extraction layer 105 by a conductive adhesive 108. The solid electrolytic capacitor 120 is formed by a molding step in which the capacitor element is placed into a mold for resin molding with the anode terminal 107 and the cathode terminal 109 fixed and then encapsulated with a resin outer package 111. In such a solid electrolytic capacitor 120, a region 100a of the anode 101 in the vicinity of an anode surface 101a out of which the anode lead 102 extends is susceptible to stress from the anode lead 102 and the resin outer package 111 upon attachment of the anode terminal 107 and in an assembly step, such as a molding step, so that the dielectric layer 103 formed on the surface of the anode 101 in the region 100a will be likely to cause defects, such as cracks.
To cope with the above problem, a solid electrolytic capacitor described in JP-A H02-277213 proposes a technique in which the dielectric layer formed on the anode 101 has an increased thickness over the entire region 100a described above to prevent the occurrence of cracks due to stress in the dielectric layer formed on the surface of the anode 101 in the above region 100a and thereby reduce the leakage current.